Steric effects in the adsorption of O₂ on a Cu(111) surface

Probing the stereodynamics of a gas-surface interaction is a useful tool to investigate the mechanisms responsible for adsorption. Experimental results are provided on the adsorption of alignment-controlled O₂ interacting with a Cu(111) surface for the first time, across a range of incident energies (65-550 meV) and angles of incidence (0-60°). Molecules of O₂ in a supersonic beam are prepared in a single spin-rotational state, and aligned with a Cu(111) surface so that the rotational angular momentum of O₂ is either parallel or perpendicular to the surface. A strong steric effect is observed, where the initial sticking probability is higher in the case of a 'side-on' collision, with measurable adsorption appearing at normal incident energies of 100 meV. The onset of sticking occurs at incident energies of approximately 200 meV in the case of an 'end-on' collision. The results also indicate that the adsorption of O₂ on Cu(111) is predominantly due to an activated process in the energy range probed, corroborating previous experimental and theoretical results.